Encoding apparatus and decoding apparatus for depth image, and encoding method and decoding method

ABSTRACT

Disclosed are an encoding apparatus and decoding apparatus for a depth image and an encoding method and decoding method. To process a depth image according to an intra prediction mode, the encoding apparatus or the decoding apparatus may use a representative mode from a DC mode of an SDC mode, a planar mode, or DMM 1 . Further, to process the depth image according to an intra prediction mode, the encoding apparatus or the decoding apparatus may use a representative mode from a planar mode or DMM 1.

TECHNICAL FIELD

The following embodiments relate to processing of a depth image based ona simplified depth coding (SDC) mode when the depth image is encoded ordecoded. In particular, embodiments may be applicable to a videocompression field in which a bit rate of a depth image needs to bereduced due to a limited bandwidth.

BACKGROUND ART

To encode or decode a depth image, an intra prediction or an interprediction may be used. The intra prediction may be performed based on aspatial correlation between coding units, and the inter predictionscheme may be performed based on a temporal correlation between codingunits.

In a compression scheme according to a related art, to perform an intraprediction of a depth image, a plurality of modes may be set and acoding mode with the lowest cost may be applied to a coding unit.However, because the depth image has a specific gray level among graylevels of “0” to “255,” a more efficient coding mode may need to be setto reduce a bit rate required when the depth image is transmitted.

DISCLOSURE OF INVENTION Technical Goals

An aspect of embodiments provides a method and apparatus for processinga coding unit based on one representative mode among a Depth Coding (DC)mode, a planar mode and a depth modeling mode 1 (DMM1) in a SimplifiedDepth Coding (SDC) mode when a depth image is encoded or decoded basedon an intra prediction mode. Here, DC mode is defined to DirectComponent mode, and SDC mode is defined to Segment-wise Direct Componentmode.

Another aspect of embodiments provides a method and apparatus forprocessing a coding unit based on one representative mode among a planarmode and a DMM1 in an SDC mode when a depth image is encoded or decodedbased on an intra prediction mode.

Still another aspect of embodiments provides a method and apparatus forencoding or decoding a current block corresponding to a coding unit of adepth image based on an SDC mode of an upper block or a left blockneighboring the current block.

TECHNICAL SOLUTIONS

According to an aspect, there is provided a method of encoding a depthimage, the method including: encoding a coding unit of the depth imagebased on a simplified depth coding (SDC) mode; and generating abitstream including the SDC mode applied to the coding unit and residualinformation of the coding unit, wherein the SDC mode includes a planarmode or a depth modeling mode 1 (DMM1).

The encoding may include encoding the coding unit based on an SDC modeof an upper block or a left block neighboring a current blockcorresponding to the coding unit.

The residual information of the coding unit may be mapped to an indexbased on a depth lookup table (DLT) generated for each frame of thedepth image.

According to another aspect, there is provided a method of encoding adepth image, the method including: encoding a coding unit of the depthimage based on an SDC mode; and generating a bitstream including the SDCmode applied to the coding unit and residual information of the codingunit, wherein the SDC mode includes a depth coding (DC) mode, a planarmode or a DMM1.

The encoding may include encoding the coding unit based on an SDC modeof an upper block or a left block neighboring a current blockcorresponding to the coding unit.

The residual information of the coding unit may be mapped to an indexbased on a DLT generated for each frame of the depth image.

According to another aspect, there is provided a method of decoding adepth image, the method including: determining an SDC mode associatedwith an intra prediction applied to a coding unit of the depth image;and decoding the coding unit based on the SDC mode, wherein the SDC modeincludes a planar mode or a DMM1.

The planar mode may be an SDC mode using an original depth value and apredicted depth value based on a top-left sample, a top-right sample, abottom-left sample and a bottom-right sample among a plurality ofsamples included in the coding unit.

The DMM1 may be an SDC mode using an original depth value and apredicted depth value of each segment derived from a top-left sample, atop-right sample, a bottom-left sample and a bottom-right sample thatbelong to the same segment in the coding unit.

According to another aspect, there is provided a method of decoding adepth image, the method including: determining an SDC mode associatedwith an intra prediction applied to a coding unit of the depth image;and decoding the coding unit based on the SDC mode, wherein the SDC modeincludes a DC mode, a planar mode or a DMM1.

The planar mode may be an SDC mode using an original depth value and apredicted depth value based on a top-left sample, a top-right sample, abottom-left sample and a bottom-right sample among a plurality ofsamples included in the coding unit.

The DMM1 may be an SDC mode using an original depth value and apredicted depth value of each segment derived from a top-left sample, atop-right sample, a bottom-left sample and a bottom-right sample thatbelong to the same segment in the coding unit.

According to another aspect, there is provided a method of decoding adepth image, the method including: determining an SDC mode associatedwith an intra prediction applied to a coding unit of the depth image;and decoding the coding unit based on the SDC mode, wherein the SDC modecomprises a planar mode, a depth modeling mode 1 (DMM1) and a depthmodeling mode 2 (DMM2), and wherein a depth coding (DC) mode is excludedfrom the SDC mode.

According to another aspect, there is provided a method of decoding adepth image, the method including: determining an SDC mode associatedwith an intra prediction applied to a coding unit of the depth image;and decoding the coding unit based on the SDC mode, wherein the SDC modecomprises a planar mode, and a depth modeling mode 1 (DMM1), wherein adepth coding (DC) mode and a depth modeling mode 2 (DMM2) are excludedfrom the SDC mode.

According to another aspect, there is provided an apparatus for encodinga depth image, the apparatus including a processor, wherein theprocessor performs: encoding a coding unit of the depth image based onan SDC mode; and generating a bitstream including the SDC mode appliedto the coding unit and residual information of the coding unit, andwherein the SDC mode includes a planar mode or a DMM1.

According to another aspect, there is provided an apparatus for encodinga depth image, the apparatus including a processor, wherein theprocessor performs: encoding a coding unit of the depth image based onan SDC mode; and generating a bitstream including the SDC mode appliedto the coding unit and residual information of the coding unit, andwherein the SDC mode includes a DC mode, a planar mode or a DMM1.

According to another aspect, there is provided an apparatus for decodinga depth image, the apparatus including a processor, wherein theprocessor performs: determining an SDC mode associated with an intraprediction applied to a coding unit of the depth image; and decoding thecoding unit based on the SDC mode, and wherein the SDC mode includes aplanar mode or a DMM1.

According to another aspect, there is provided an apparatus for decodinga depth image, the apparatus including a processor, wherein theprocessor performs: determining an SDC mode associated with an intraprediction applied to a coding unit of the depth image; and decoding thecoding unit based on the SDC mode, and wherein the SDC mode includes aDC mode, a planar mode or a DMM1.

According to another aspect, there is provided an apparatus for decodinga depth image, the apparatus including a processor, wherein theprocessor performs: determining an SDC mode associated with an intraprediction applied to a coding unit of the depth image; and decoding thecoding unit based on the SDC mode, and wherein the SDC mode comprises aplanar mode, a depth modeling mode 1 (DMM1) and a depth modeling mode 2(DMM2), and wherein a depth coding (DC) mode is excluded from the SDCmode.

According to another aspect, there is provided an apparatus for decodinga depth image, the apparatus including a processor, wherein theprocessor performs: determining an SDC mode associated with an intraprediction applied to a coding unit of the depth image; and decoding thecoding unit based on the SDC mode, and wherein the SDC mode comprises aplanar mode, and a depth modeling mode 1 (DMM1), wherein a depth coding(DC) mode and a depth modeling mode 2 (DMM2) are excluded from the SDCmode.

Effects of the Invention

According to embodiments, a coding unit may be processed based on onerepresentative mode among a depth coding (DC) mode, a planar mode and adepth modeling mode 1 (DMM1) in a simplified depth coding (SDC) modewhen a depth image is encoded or decoded based on an intra predictionmode and thus, it is possible to enhance an efficiency of processing thecoding unit.

Additionally, according to embodiments, a coding unit may be processedbased on one representative mode among a planar mode and a DMM1 in anSDC mode when a depth image is encoded or decoded based on an intraprediction mode and thus, it is possible to enhance an efficiency ofprocessing the coding unit.

Furthermore, according to embodiments, a current block corresponding toa coding unit of a depth image may be encoded or decoded based on an SDCmode of an upper block or a left block neighboring the current block andthus, it is possible to more effectively reflect a characteristic of thedepth image.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an encoding apparatus and a decodingapparatus according to an embodiment.

FIG. 2 is a flowchart illustrating an operation of an encoding apparatusaccording to an embodiment.

FIG. 3 is a flowchart illustrating an operation of a decoding apparatusaccording to an embodiment.

FIG. 4 is a diagram provided to explain a depth modeling mode 1 (DMM1)according to an embodiment.

FIG. 5 is a diagram illustrating a process of deriving a predicted valuebased on a planar mode according to an embodiment.

FIG. 6 is a diagram illustrating a process of deriving a predicted valuebased on a DMM1 according to an embodiment.

FIG. 7 is a diagram illustrating a process of determining a coding modeof a current block according to an embodiment.

FIG. 8 is a diagram illustrating enable_flag used to compensate for adepth lookup table (DLT) according to an embodiment.

FIG. 9 is a diagram illustrating an example of a DLT in a slice headeraccording to an embodiment.

FIG. 10 is a diagram illustrating another example of a DLT in a sliceheader according to an embodiment.

DETAILED DESCRIPTION FOR CARRYING OUT THE INVENTION

The following detailed description is provided in order to explain theembodiments by referring to the figures.

FIG. 1 is a diagram illustrating an encoding apparatus and a decodingapparatus according to an embodiment.

Referring to FIG. 1, an encoding apparatus 101 may transmit a bitstreamgenerated by encoding a depth image to a decoding apparatus 102.Alternatively, the encoding apparatus 101 may encode a depth image, andmay store the depth image in a recoding medium or store the depth imagein a separate file format. The decoding apparatus 102 may derive thedepth image from the bitstream, and may play back a three-dimensional(3D) image. Because a bandwidth used to transmit the bitstream islimited, a bit rate of the depth image may need to be reduced. The depthimage may be expressed as a depth map.

For example, the encoding apparatus 101 may encode the depth image usingan intra prediction. The encoding apparatus 101 may encode the depthimage based on an image compression scheme, for example, H.264/advancedvideo coding (AVC), H.264/multiview video coding (MVC) or highefficiency video coding (HEVC). The encoding apparatus 101 may partitiona single depth image into a plurality of coding units, and may performthe intra prediction based on a spatial correlation between the codingunits or perform an inter prediction based on a temporal correlationbetween the coding units.

The intra prediction may be predicting a pixel value of a coding unit tobe encoded from pixel values of pixels neighboring the coding unit. Apredicted value of the coding unit calculated through the intraprediction may vary based on a size of the coding unit and a scheme ofreferring to neighboring pixels used for prediction.

In the image compression scheme, a type of intra prediction modes may bedefined based on a size of a coding unit and a scheme of referring toneighboring pixels. The encoding apparatus 101 may select one of theintra prediction modes defined in the image compression scheme, and mayencode a coding unit. The encoding apparatus 101 may select an intraprediction mode to minimize a bit rate used to encode the coding unitand a distortion of a decoded coding unit. For example, the encodingapparatus 101 may perform encoding based on all the intra predictionmodes defined in the image compression scheme, and may select an intraprediction mode with the lowest cost for the encoding as an encodingmode of a coding unit.

When the depth image is encoded based on the intra prediction, theencoding apparatus 101 may generate a depth lookup table (DLT). The DLTmay represent a specific gray level by an index based on acharacteristic of the depth image. A scheme of increasing an encodingefficiency by representing residual information and a pixel value of acoding unit using an index may be defined as a simplified depth coding(SDC). The depth image may include pixels corresponding specific graylevels among gray levels of “0” to “255” and accordingly, the encodingefficiency may be enhanced when encoding is performed based on an SDCmode.

The encoding apparatus 101 may use a representative mode defined in theSDC mode to encode the depth image. The representative mode may include,for example, a depth coding (DC) mode, a depth modeling mode 1 (DMM1), adepth modeling mode 2 (DMM2), and a planar mode. For example, theencoding apparatus 101 may perform encoding based on threerepresentative modes excluding the DMM2 from four representative modes.In addition, the encoding apparatus 101 may perform encoding based ontwo representative modes excluding the DC mode and the DMM2 from thefour representative modes.

The encoding apparatus 101 may set a representative mode to a codingunit. The encoding apparatus 101 may transfer the representative modeand residual information to the decoding apparatus 102. The residualinformation may be a result obtained by predicting the coding unit.

FIG. 2 is a flowchart illustrating an operation of an encoding apparatusaccording to an embodiment.

In operation 201, the encoding apparatus 101 may encode a coding unitbased on an SDC mode. To encode the depth image based on the SDC mode,the encoding apparatus 101 may use a few representative modes, insteadof using 35 intra prediction modes that are generally used in the HEVC.The depth image may be less complex than a color image and gray levelsof the depth image may be distributed in a predetermined range andaccordingly, most predictions may be enabled based on a simplerepresentative mode.

The SDC mode may be associated with an intra prediction mode used toencode a depth image to play back a 3D video. In an example, to encodethe depth image, the encoding apparatus 101 may use one of the planarmode and the DMM1 excluding the DC mode and the DMM2 from the SDC mode.In other words, the planar mode and the DMM1 may be representative modesin the SDC mode.

In another example, to encode the depth image, the encoding apparatus101 may use one of the DC mode, the planar mode and the DMM1 excludingthe DMM2 from the SDC mode. In other words, the DC mode, the planar modeand the DMM1 may be representative modes in the SDC mode. The encodingapparatus 101 may predict and encode a coding unit based on arepresentative mode with the highest probability among therepresentative modes in the SDC mode.

The DC mode may indicate a directional intra prediction in a depth imagecompression scheme according to a related art. A DMM mode may be used toenhance a distortion rate and a bit rate at a point in time whensynthesis is performed during modeling of discontinuities of a depthimage. In other words, the encoding apparatus 101 may encode the depthimage based on the SDC mode from which a portion of the representativemodes is excluded and thus, it is possible to enhance an encodingefficiency.

When an SDC mode for a coding unit is selected, the coding unit may bepredicted based on a representative mode of the selected SDC mode.Because prediction is performed based on the SDC mode in one or twodepth segments for each coding unit, a single residual DC depth valuemay be coded to each of the depth segments. A depth segment may includea plurality of pixels. When the SDC mode is used, residual informationmay be coded in a pixel domain, and accordingly ringing artifacts may beremoved.

The SDC mode may be used for intra prediction of a depth image. An SDCflag indicating that the SDC mode is applied to a coding unit may beadditionally used. For example, when a coding unit is encoded based onthe SDC mode, a size of the coding unit may be determined as “2N×2N.”When encoding is performed based on the SDC mode, a representative modeand a segment type of the coding unit may be encoded.

<Representative Mode/Segment Type>

-   -   DC (1 segment)    -   DMM Mode 1—Explicit Wedgelets (2 segments)    -   DMM Mode 2—Intra-Predicted Wedgelets (2 segments)    -   Planar (1 segment)

For each segment, residual information in a pixel domain may be signaledin a bitstream. Before encoding, the residual information may be mappedto an original depth value of an unencoded depth image using a DLT.Accordingly, the residual information may be encoded by signaling anindex in the DLT.

The encoding apparatus 101 may analyze a histogram by extracting apredetermined number of frames from a plurality of frames of the depthimage, and may determine a gray level. The encoding apparatus 101 maygenerate a DLT shown below, based on the determined gray level.

index gray level 0 4 1 7 2 12 . . . 50 130

For example, the encoding apparatus 101 may encode a coding unit in theSDC mode. In this example, the encoding apparatus 101 may combine DLTsand may signal residual information set for each segment, to reduce arequired bit rate. The DLT may be a result of mapping original depthvalues of a depth image to indices. The DLT may be generated byanalyzing a specific number of frames from a sequence of an input depthimage. The DLT may be used in an encoding process to reduce a bit depthof the residual information.

The encoding apparatus 101 may analyze a specific number of frames froma sequence of a depth image. The frames may be encoded, and all pixelsmay be scanned for all depth values. During the analyzing, the encodingapparatus 101 may map depth values to valid depth values based on anoriginal depth image that is not compressed, and may generate a mappingtable.

However, when a DLT is generated by analyzing a predetermined number offrames, instead of analyzing all frames in a depth image, whether theDLT represents the depth image may be a problem. For example, theencoding apparatus 101 may generate a DLT by analyzing a depth image,and may record the DLT in a sequence parameter set (SPS). The DLTrecorded in the SPS may be transmitted to the decoding apparatus 102.

-   -   The DLT may be generated based on the following process:    -   Input: Depth map D_t of N×M pixels at time instance t    -   Output: depth lookup table D(.)    -   Index Lookup Table I(.)    -   Depth Mapping Table M(.)    -   Number of valid depth values d_valid

<Algorithm>

-   -   Initialization    -   boolean vector B(d)=FALSE for all depth values d    -   index counter i=( )    -   Process each pixel position p in D_t for multiple time instances        t:    -   Set B(D_t(p))=TRUE to mark valid depth values    -   Count number of TRUE values in B(d)? d_valid    -   For each d with B(d)==TRUE:    -   Set D(i)=d    -   Set M(d)=d    -   Set I(d)=i    -   i=i+1    -   For each d with B(d)==FALSE:    -   Find d□=arg min|d−d□| and B(d□)==TRUE    -   Set M(d)=d□    -   Set I(d)=I(d□)

The encoding apparatus 101 may map a depth image to an indexcorresponding to a depth value, instead of encoding residual informationof the depth image for a given coding unit. A mapping table may betransmitted to the decoding apparatus 102 configured to derive the depthvalue from the index through an inverse of the DLT.

-   -   Input: Original depth value d_orig    -   Predicted depth value d_pred    -   Index Lookup Table I(.)    -   Number of valid depth values d_valid    -   Output: Residual index i_resi to be coded    -   Algorithm:    -   i_resi=I(d_orig)−I(d_pred)    -   An index i_resi of the residual information may be encoded with        a flag.

The encoding apparatus 101 may determine an SDC mode to be applied to acurrent block corresponding to a coding unit, using a block neighboringthe current block. For example, the encoding apparatus 101 may determinean SDC mode of an upper block or a left block neighboring the currentblock, and may determine an SDC mode of the current block. When theupper block or the left block is encoded using an inter prediction modeor an intra prediction mode, instead of using the SDC mode, the encodingapparatus 101 may perform exception processing.

In operation 202, the encoding apparatus 101 may transfer a bitstreamincluding residual information of the coding unit and the SDC modeapplied to the coding unit to the decoding apparatus 102.

FIG. 3 is a flowchart illustrating an operation of a decoding apparatusaccording to an embodiment.

In operation 301, the decoding apparatus 102 may determine an SDC modeapplied to a coding unit. In an example, the decoding apparatus 102 maydetermine whether one of a planar mode and a DMM1 excluding a DMM2 and aDC mode from the SDC mode is applied to the coding unit. In other words,the DMM1 and the planar mode may be representative modes in the SDCmode.

In another example, the decoding apparatus 102 may determine whether oneof a DC mode, a planar mode and a DMM1 excluding a DMM2 from the SDCmode is applied to the coding unit to encode a depth image. In otherwords, the DC mode, the DMM1 and the planar mode may be representativemodes in the SDC mode.

In operation 302, the decoding apparatus 102 may decode the coding unitbased on the SDC mode applied to the coding unit.

FIG. 4 is a diagram provided to explain a DMM1 according to anembodiment.

A depth image may mainly include sharp edges representing an objectborder, and nearly constant or slowly varying sample values thatrepresent object regions. To clearly express the object border in thedepth image, an intra prediction mode for the depth image may be added.A block 401 of a depth image may be partitioned into two non-rectangularregions, and each of the non-rectangular regions may be represented by aconstant. Samples corresponding to each of the non-rectangular regionsmay be specified by a constant, and each of the non-rectangular regionsmay be represented by a constant partition value (CPV). A Wedgeletpartitioning scheme and a Contour partitioning scheme may be used as apartitioning scheme, and the DMM1 may be based on the Wedgeletpartitioning scheme.

Based on an SDC mode, residual information indicating a differencebetween an original depth value and a predicted depth value may betransmitted. In a block of a depth image, a predicted depth value may bedetermined based on a DMM. In the Wedgelet partitioning scheme, theblock 401 of the depth image may be partitioned into two regions P1 andP2 by a straight line. A block 402 of the depth image may include aplurality of samples (uB×vB), and each of the samples may belong to oneof the two regions.

In addition, samples in a block 403 of the depth image may be identifiedby binary information based on a region to which each of the samples inthe block 403 belongs. The DMM1 may be based on the Wedgeletpartitioning scheme, and partition information may be transmittedthrough a bitstream to the decoding apparatus 102. The decodingapparatus 102 may restore a block of the depth image based on thepartition information.

The partition information may be transmitted by the encoding apparatus101 to the decoding apparatus 102, instead of being predicted by thedecoding apparatus 102. A boundary based on the Wedgelet partitioningscheme may be determined to minimize a distortion between the originaldepth value and a predicted value belonging to a region obtained by theWedgelet partitioning scheme.

FIG. 5 is a diagram illustrating a process of deriving a predicted valuebased on a planar mode according to an embodiment.

An SDC mode may replace an intra prediction mode of a depth image. Adepth intra parameter of the depth image may indicate whether a codingunit is signaled in the SDC mode. In the SDC mode, a block correspondingto a coding unit of the depth image may be predicted based on one of aplanar mode and a DMM1 included in the SDC mode. Also, in the SDC mode,a block corresponding to a coding unit of the depth image may bepredicted based on one of a planar mode, a DC mode and a DMM1 includedin the SDC mode.

A coding unit including a prediction unit predicted based on the SDCmode may have a partition size of “2N×2N.” Residual information may becoded by quantized transform coefficients, and residual informationindicating one or two constants may be signaled.

A block coded based on the SDC mode may be signaled based on thefollowing information:

-   -   DMM Mode 1—Explicit Wedgelets (2 segments)    -   Planar (1 segment)

Before encoding, residual information may be mapped to an original depthvalue of a depth image based on a DLT. The residual information may becoded by signaling an index in the DLT. A DLT representing a mappingtable may be transmitted to the decoding apparatus 102.

The encoding apparatus 101 may use an average value of a predicted depthvalue d_(pred) and an original depth value d_(orig) of the depth image.In a planar mode, the predicted depth value d_(pred) may be calculatedas an average value of a top-left sample 501, a bottom-left sample 502,a top-right sample 503 and a bottom-right sample 504 in a predictionblock.

FIG. 6 is a diagram illustrating a process of deriving a predicted valuebased on a DMM1 according to an embodiment.

In the DMM1, a predicted depth value d_(pred) corresponding to a regionmay be determined as an average value of samples belonging to the regionin a prediction block. For example, a predicted depth value d_(pred)corresponding to a region including white samples may be determined as atop-left sample 601. Additionally, a predicted depth value d_(pred)corresponding to a region including black samples may be calculated asan average value of a bottom-left sample 602, a top-right sample 603 anda bottom-right sample 604. A region may correspond to a segment.

A DLT may be used to map an original depth value to a predicted depthvalue using an index. A residual index iresi may be transmitted to thedecoding apparatus 102, and may be determined based on the followingEquation 1:

t _(resi) =I(d _(orig))−I(d _(pred)),  [Equation 1]

Here, I(.) denotes a DLT. In the decoding apparatus 102, an averagevalue of the restored original depth values may be determined based onthe following Equation 2:

{circumflex over (d)} _(orig) =I ⁻¹(I(d _(pred))+i _(resi)),  [Equation2]

Here, I(.) denotes an inverse DLT. Average residual information may bedetermined based on the following Equation 3:

{circumflex over (d)} _(resi) ={circumflex over (d)} _(orig) −d_(pred).  [Equation 3]

A restored sample P_(x,y) may be determined based on the followingEquation 4:

{circumflex over (P)} _(x,y) =P _(x,y) +{circumflex over (d)}_(resi).  [Equation 4]

The calculated residual information may be encoded with a flag.

FIG. 7 is a diagram illustrating a process of determining a coding modeof a current block according to an embodiment.

As described above with reference to FIG. 2, the encoding apparatus 101may determine a coding mode of a current block X 701 corresponding to acoding unit. The encoding apparatus 101 may determine the coding mode ofthe current block 701 based on an SDC mode applied to a left block A 702or an upper block B 703 neighboring the current block 701.

For example, when a DC mode in the SDC mode is applied to the left block702, the DC mode may be applied to the current block 701. When a DMM1 inthe SDC mode is applied to the left block 702, the DMM1 may be appliedto the current block 701. When a planar mode in the SDC mode is appliedto the left block 702, the planar mode may be applied to the currentblock 701. The same mode as a mode applied to the upper block 703 may beapplied to the current block 701.

When an inter prediction mode or an intra prediction mode other than theSDC mode is applied to the left block 702 or the upper block 703, the DCmode may be applied to the current block 701.

FIG. 8 is a diagram illustrating enable_flag used to compensate for aDLT according to an embodiment.

The encoding apparatus 101 may extract a preset number of frames from asequence of a depth image to be encoded, and may analyze a histogram.The encoding apparatus 101 may determine a gray level by analyzing thehistogram, and may generate a DLT based on the determined gray level.

To reflect characteristics of frames other than the preset number offrames, the encoding apparatus 101 may determine and record enable_flagfor each of frames of the depth image.

A DLT may be recorded in an SPS. The DLT recorded in the SPS may betransmitted to the decoding apparatus 102. The decoding apparatus 102may generate a DLT of a current frame of the depth image by analyzingthe current frame. The encoding apparatus 101 may compare a gray levelof the DLT recorded in the SPS to a gray level of the generated DLT.When a similarity between the gray levels is equal to or greater than areference value, the encoding apparatus 101 may perform encoding basedon an SDC mode, using the DLT recorded in the SPS without a change.Similarly, the decoding apparatus 102 may compare a gray level of theDLT recorded in the SPS to a gray level of the generated DLT. When asimilarity between the gray levels is equal to or greater than areference value, the decoding apparatus 102 may perform decoding basedon an SDC mode, using the DLT recorded in the SPS without a change.

When the similarity is less than the reference value, the encodingapparatus 101 may not process a coding unit of the depth image based onthe SDC mode. Similarly, when the similarity is less than the referencevalue, the decoding apparatus 102 may not process a coding unit of thedepth image based on the SDC mode.

When a similarity between a DLT of a current frame and the DLT recordedin the SPS is determined to be equal to or greater than a referencevalue through a comparison between the DLTs, dlt_enable_flag may be “1,”and the encoding apparatus 101 or the decoding apparatus 102 may processthe coding unit based on the SDC mode. Conversely, when the similaritybetween the DLT of the current frame and the DLT recorded in the SPS isdetermined to be less than the reference value through the comparisonbetween the DLTs, dlt_enable_flag may be “0,” and the encoding apparatus101 or the decoding apparatus 102 may not process the coding unit basedon the SDC mode.

FIG. 9 is a diagram illustrating an example of a DLT in a slice headeraccording to an embodiment.

The DLT of FIG. 8 may be generated for each frame, and may be recordedin the slice header, instead of an SPS.

FIG. 10 is a diagram illustrating another example of a DLT in a sliceheader according to an embodiment.

In FIG. 10, a DLT may be recorded in both an SPS and a slice header.When a similarity between a DLT associated with a frame and a DLTrecorded in the SPS is determined to be equal to or greater than areference value through a comparison between the DLTs, the DLTassociated with the frame may be recorded in the SPS, not in the sliceheader.

In other words, when a similarity between a DLT of a current frame and aDLT recorded in the SPS is determined to be equal to or greater than areference value through a comparison between the DLTs, dlt_enable_flagmay be “1,” and the DLT recorded in the SPS may be used. Conversely,when the similarity is determined to be less than the reference value,dlt_enable_flag may be “0,” and the DLT recorded in the SPS may not beused.

The units described herein may be implemented using hardware components,software components, and/or a combination thereof. The units andcomponents may be implemented using one or more general-purpose orspecial purpose computers, such as, for example, a processor, acontroller and an arithmetic logic unit (ALU), a digital signalprocessor, a microcomputer, a field programmable array (FPA), aprogrammable logic unit (PLU), a microprocessor or any other devicecapable of responding to and executing instructions in a defined manner.A processing device may run an operating system (OS) and one or moresoftware applications that run on the OS. The processing device also mayaccess, store, manipulate, process, and create data in response toexecution of the software. For purpose of simplicity, the description ofa processing device is used as singular; however, one skilled in the artwill appreciated that a processing device may include multipleprocessing elements and multiple types of processing elements. Forexample, a processing device may include multiple processors or aprocessor and a controller. In addition, different processingconfigurations are possible, such a parallel processors.

Software may include a computer program, a piece of code, aninstruction, or some combination thereof, to independently orcollectively instruct or configure the processing device to operate asdesired. Software and/or data may be embodied permanently or temporarilyin any type of machine, component, physical or virtual equipment,computer storage medium or device, or in a propagated signal wavecapable of providing instructions or data to or being interpreted by theprocessing device. The software also may be distributed over networkcoupled computer systems so that the software is stored and executed ina distributed fashion. The software and data may be stored by one ormore non-transitory computer readable recording mediums.

The method according to the above-described embodiments may be recordedin non-transitory computer-readable media including program instructionsto implement various operations embodied by a computer. The media mayalso include, alone or in combination with the program instructions,data files, data structures, and the like. The program instructionsrecorded on the media may be those specially designed and constructedfor the purposes of the embodiments, or they may be of the kindwell-known and available to those having skill in the computer softwarearts. Examples of non-transitory computer-readable media includemagnetic media such as hard disks, floppy disks, and magnetic tape;optical media such as CD ROM disks and DVDs; magneto-optical media suchas optical discs; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory (ROM),random access memory (RAM), flash memory, and the like. Examples ofprogram instructions include both machine code, such as produced by acompiler, and files containing higher level code that may be executed bythe computer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations of the above-described embodiments, or vice versa.

While various embodiments have been described above and in the drawings,it should be understood that they have been presented only as examples,and not as limitations. It should be understood that variousmodifications may be made the description by one of ordinary skill inthe art. For example, suitable results may be achieved if the describedtechniques are performed in a different order and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner and/or replaced or supplemented by other components ortheir equivalents. Accordingly, other implementations are within thescope of the following claims.

1. A method of encoding a depth image, the method comprising: encoding acoding unit of the depth image in a simplified depth coding (SDC) mode;and generating a bitstream comprising the SDC mode applied to the codingunit and residual information of the coding unit, wherein the SDC modecomprises a planar mode or a depth modeling mode 1 (DMM1).
 2. The methodof claim 1, wherein the encoding comprises encoding the coding unitbased on an SDC mode of an upper block or a left block neighboring acurrent block corresponding to the coding unit.
 3. The method of claim1, wherein the residual information of the coding unit is mapped to anindex based on a depth lookup table (DLT) generated for each frame ofthe depth image.
 4. A method of encoding a depth image, the methodcomprising: encoding a coding unit of the depth image based on asimplified depth coding (SDC) mode; and generating a bitstreamcomprising the SDC mode applied to the coding unit and residualinformation of the coding unit, wherein the SDC mode comprises a depthcoding (DC) mode, a planar mode or a depth modeling mode 1 (DMM1). 5.The method of claim 4, wherein the encoding comprises encoding thecoding unit based on an SDC mode of an upper block or a left blockneighboring a current block corresponding to the coding unit.
 6. Themethod of claim 4, wherein the residual information of the coding unitis mapped to an index based on a depth lookup table (DLT) generated foreach frame of the depth image.
 7. A method of decoding a depth image,the method comprising: determining a simplified depth coding (SDC) modeassociated with an intra prediction applied to a coding unit of thedepth image; and decoding the coding unit based on the SDC mode, whereinthe SDC mode comprises a planar mode or a depth modeling mode 1 (DMM1).8. The method of claim 7, wherein the planar mode is an SDC mode usingan original depth value and a predicted depth value based on a top-leftsample, a top-right sample, a bottom-left sample and a bottom-rightsample among a plurality of samples included in the coding unit.
 9. Themethod of claim 7, wherein the DMM1 is an SDC mode using an originaldepth value and a predicted depth value of each segment derived from atop-left sample, a top-right sample, a bottom-left sample and abottom-right sample that belong to the same segment in the coding unit.10. A method of decoding a depth image, the method comprising:determining a simplified depth coding (SDC) mode associated with anintra prediction applied to a coding unit of the depth image; anddecoding the coding unit based on the SDC mode, wherein the SDC modecomprises a depth coding (DC) mode, a planar mode or a depth modelingmode 1 (DMM1).
 11. The method of claim 10, wherein the planar mode is anSDC mode using an original depth value and a predicted depth value basedon a top-left sample, a top-right sample, a bottom-left sample and abottom-right sample among a plurality of samples included in the codingunit.
 12. The method of claim 10, wherein the DMM1 is an SDC mode usingan original depth value and a predicted depth value of each segmentderived from a top-left sample, a top-right sample, a bottom-left sampleand a bottom-right sample that belong to the same segment in the codingunit.
 13. A method of decoding a depth image, the method comprising:determining a simplified depth coding (SDC) mode associated with anintra prediction applied to a coding unit of the depth image; anddecoding the coding unit based on the SDC mode, wherein the SDC modecomprises a planar mode, a depth modeling mode 1 (DMM1) and a depthmodeling mode 2 (DMM2), and wherein a depth coding (DC) mode is excludedfrom the SDC mode.
 14. A method of decoding a depth image, the methodcomprising: determining a simplified depth coding (SDC) mode associatedwith an intra prediction applied to a coding unit of the depth image;and decoding the coding unit based on the SDC mode, wherein the SDC modecomprises a planar mode, and a depth modeling mode 1 (DMM1), wherein adepth coding (DC) mode and a depth modeling mode 2 (DMM2) are excludedfrom the SDC mode.
 15. An apparatus for encoding a depth image, theapparatus comprising a processor, wherein the processor performs:encoding a coding unit of the depth image based on a simplified depthcoding (SDC) mode; and generating a bitstream comprising the SDC modeapplied to the coding unit and residual information of the coding unit,and wherein the SDC mode comprises a planar mode or a depth modelingmode 1 (DMM1).
 16. An apparatus for encoding a depth image, theapparatus comprising a processor, wherein the processor performs:encoding a coding unit of the depth image based on a simplified depthcoding (SDC) mode; and generating a bitstream comprising the SDC modeapplied to the coding unit and residual information of the coding unit,and wherein the SDC mode comprises a depth coding (DC) mode, a planarmode or a depth modeling mode 1 (DMM1).
 17. An apparatus for decoding adepth image, the apparatus comprising a processor, wherein the processorperforms: determining a simplified depth coding (SDC) mode associatedwith an intra prediction applied to a coding unit of the depth image;and decoding the coding unit based on the SDC mode, and wherein the SDCmode comprises a planar mode or a depth modeling mode 1 (DMM1).
 18. Anapparatus for decoding a depth image, the apparatus comprising aprocessor, wherein the processor performs: determining a simplifieddepth coding (SDC) mode associated with an intra prediction applied to acoding unit of the depth image; and decoding the coding unit based onthe SDC mode, and wherein the SDC mode comprises a depth coding (DC)mode, a planar mode or a depth modeling mode 1 (DMM1).
 19. An apparatusfor decoding a depth image, the apparatus comprising a processor,wherein the processor performs: determining a simplified depth coding(SDC) mode associated with an intra prediction applied to a coding unitof the depth image; and decoding the coding unit based on the SDC mode,and wherein the SDC mode comprises a planar mode, a depth modeling mode1 (DMM1) and a depth modeling mode 2 (DMM2), and wherein a depth coding(DC) mode is excluded from the SDC mode.
 20. An apparatus for decoding adepth image, the apparatus comprising a processor, wherein the processorperforms: determining a simplified depth coding (SDC) mode associatedwith an intra prediction applied to a coding unit of the depth image;and decoding the coding unit based on the SDC mode, and wherein the SDCmode comprises a planar mode, and a depth modeling mode 1 (DMM1),wherein a depth coding (DC) mode and a depth modeling mode 2 (DMM2) areexcluded from the SDC mode.